Ligature

The connecting link between two letters that are joined together. Also, two or more characters that are combined into one glyph, generally comprising such characters as ﬁ, ﬂ, ﬀ, ﬃ, ﬄ etc.

When type was made of metal, ligatures were a physical necessity to stop one piece of metal clashing with another: it was physically impossible for strokes to overlap. Not so with digital strokes: so nowadays, ligatures have primarily aesthetic benefits. Some ligatures, such as the common ﬁ may merely prevent the collision of two glyphs, but others such as the OO ligature provide a decorative, ornamental quality.